Heat resisting alloy steel



Patented July 4, 1939 .UNITED STATES PATENT OFFICE 2,165,035 HEAT RESISTING ALLOY STEELv Jersey Application August 13, 1938, Serial No. 224,702

2 Claims.

Our invention relates to alloy steels which are characterized by heat resisting qualities at high temperatures, the main object being to provide an improved alloy which will advantageously combine non-scaling duality, unusual strength, and resistance to abrasion at such temperatures; and it consists essentially in employing the known alloy elements carbon, manganese, silicon' and chromium in scientifically determined critical proportions which insure the securing of the predetermined desired qualities, as fully set forth in the following specification taken in connection with the accompanying drawing and specifically defined in the subjoined claims..

In the drawing, which indicates graph charts of steel embodying our'invention, with one element varying in quantity,

Fig. 1 indicates a carbon variance.

Fig. 2 indicates a manganese variance.

Fig. 3 indicates a silicon variance, and

Fig. 4 indicates a chromium variance.

That added-scale resistance is imparted to steel by the use of chromium and silicon, singly or jointly, is well-known in the art, but to the best of our knowledge, the beneficial effectof manganese in this respect has not heretofore been recognized. We are further aware that manganese and silicon or manganese, silicon and chromium have been added to steel in various proportions for other useful purposes, but never in the critical proportions which insure predicted desirable results as provided for by our present invention, the type analysis of which is as follows:

. lPercent Carbonapproximately .40 Manganeseapproximately 8 Silicon-approximately 4.50 ChromiumL-approximately 2.75 Balance `substantially all iron.

Our tests show that this alloy possesses an unpredictably high degree of scale resistance when exposed to incandescent temperatures such as are encountered in furnaces, kilns, internal combustion engines, etc. As a means of demonstrating this high degree of scale resistance, we take machined specimens and expose them continuously in an oxidizing furnace atmosphere at 1600 F. for eight hours and -find only a slight discoloration of the surface with negligible change in weight. For convenience, We rate the scale resistance. of various alloys exposed to this test in the following empirical manner.

Scale re sistance Appearance oi the surface rating 1 -r.. Practically no scale-surface bright.

Very light powdery free scale-surface bright.

Light hgray powdery free scale-surface generally Gray fr ee scale-surface slightly discolored.

Light grayish black adhering scale. 4

Heavy black or heavy dark gray free scale-surface discolored.

Heavy gray or black adhering scale.

The critical nature of the particular analysis combination set forth may readily be proved by melting a series of alloys in which any three of the essential elements are kept constantv and the fourth element is permitted to vary above and below the optimum percentage set forth. Four such series of tests are illustrated in the drawing. Figure 1 illustrates the scale resistance of a series of alloys each of which contains manganese approximately 8%, silicon approximately 4.50%, and chromium. approximately 2.75%; and in which the carbon is permitted to varyl from practically nothing 4to over 2%.l The carbon variable is plotted horizontally, and the scale resistance number is plotted vertically. lIt will be seen that scale resistance gradually improves as the carbon is increased, reaches an effective maximum between about .20% and .75%, and then decreases as the. carbonris further increased.

Figure 2 shows the scale resistance of series of alloys each of which contains carbon approxithe silicon is permitted to vary from about 2% to A about 30%. llit Will be seen that the s cale resistance gradually improves'asthe silicon is increased, reaches an effective maximum between 3.5% and 6.5%, and then decreases as the silicon is further increased.

Figure 4 shows the scale resistance of a series of alloys each of which contains carbon approximately .40%, manganese approximately 8%, silicon approximately 4.50%; and in which the chromium is permitted to vary from substantially nothing to about 30%. It will be seen that the scale resistance gradually improves as the chromium is increased, 4reaches an effective maximum between 1.5% vand 4.5%, and then decreases as the chromium is further increased.

'To the best of our knowledge, the critical nature of this particular combination of elements with respect to scale resistance is new and such alloys have never before been made for heat resisting, scale resisting or any other purposes.

Alloys for use at elevated temperatures should not only be highly resistant to scale and surface deterioration, but should, if possible, also possess a high degree of mechanical strength at elevated temperatures. A simple criterion of strength at elevated temperatures is found in the Brinell hardness test. Specimens of the alloys being tested are heated to the desired temperature and are then subjected to the Brinell hardness test. Relatively highfBrinell hardness numerals indicate relatively high strength at that temperature. comparative scale resistance and red hardness of our new critical alloy combination and certain vother ferrous alloys which havev been extensively used for heat resisting applications.

The following table illustrates the find that the desirable scale resisting and red hard properties are usefully retained with such extra alloying elements present, alone or in combination, up to perhaps 3%. Our alloy can of course containy small percentages of phosphorus and sulphur such as are normally encountered in commercial manufacture, or these elements may be deliberately added in larger quantities for free machining purposes. In the subjoined claims, the expression balancesubstantially all iron contemplates extraneous alloys permissibly present in a total quantity of not more than about 3%.

, Our new heat resisting alloy can readily `be made in the usual steel making equipment by those familiar with the art. Electric melting in induction or arc furnaces is preferred for conservation of the alloys, appropriate charges of melting s'tock and ferrous alloys being employed. The alloy is readily malleable, and can be hot hammered or Vhot rolled into useful shapes with standard steel mill equipment. heat treated-for hardness, or softened for machining by 'suitable thermal treatment.

We have measured the scale resistance and red hardness of our new alloy in the cast, rolled, and forged condition vand nd that it can be employed in any of these forms for heat resisting purposes such as valves in internal combustion engines, high temperature bolts and studs, furnace parts, and the like.

What we claim is:

1. A heat resisting ferrous alloy having scale It will be seen that our preferred composition in alloy 908 compares very favorably with the best scale resistance and red hardness of the older alloys, combining these two desirable properties in one alloy. The excellent properties of alloy 856 are also noteworthy as embodying our critical percentages of silicon and manganese without chromium.

We have experimented with the addition vof other alloying elements to the optimum carbon, manganese, silicon, chromium combination set forth adding such elements as nickel, tungsten,

" selenium, molybdenum, vanadium, copper, alumi- `num and other common alloying elements, and

resisting property and unusual strength and resistance to abrasion at high temperatures, containing carbon about .40%, manganese about 8.00%-, silicon about 4.50%, chromium about- 2.75%, and the balance substantially all iron.

2. A heat resisting ferrous allo'y having scale resisting property and unusual strength and rehsistanc'e to abrasion at high temperatures, containing carbon between .20% and .75%, manganese between 6.00% and 10.00%, silicon between 3.5% and 6.5%, chromium between 1.5% and 4.5%, the balance substantially all iron.

` BERTON H. DE LONG.

OMAR V. GREENE.

The alloy may be 

